Someone Plz Help Soo Confused, How do you keep your GST/HST Records?

[line10trading]

Hello Everyone,

I have been selling on eBay since early this year and now I have decided to volunteerly register for GST/HST account to collect Input Tax Credits, I'm very curious to know how everyone else keeps their records, any recommended software? 

one problem I'm having is that when I download a excel report from paypal it shows you all the payments from all over the world, is there anyway to seperate candian customers and US customers on paypal report?

What kind of supporting document should I keep? especially for exports because I need to prove that the item is exported and I don't have to Collect HST/GST

One more thing to note, on eBay I'm registered as a USA seller because I take my shipments to Niagara Falls to ship with USPS 

Any help would be much much appreciated,